The invention relates to plastics which are self-disinfecting. The invention relates in particular to dental plastics and impression materials in which a biocidal material is incorporated and the adhesivity of whose surface vis-à-vis microorganisms is reduced.
Disinfection is a permanent requirement in dental practices and dental engineering laboratories. The transmission of germs from contaminated gloves or even bare hands via equipment, tools or materials to humans presents an enormous risk for the patient, the dentist or dental technician and their assistants. Particularly in daily procedures in practice, the patient can come into contact with contaminated items or objects, microorganisms being able to enter the blood stream through open wounds. During a session, as a result for example of using contaminated gloves when mixing an impression material and using contaminated optical conductors for the light polymerisation of radiation-curable filling materials, the risk of infection can be increased. Although the hygiene regulations are very strict, no absolutely reliable protection against infection can be guaranteed.
The use of biocidal substances is known in other fields, for example the preparation of plasticized polyvinyl chloride for use as a swimming pool cleaner, (C. R. Jones, P. S. Handley, G. D. Robson, I. M. Eastwood and M. Greenhalgh xe2x80x9cBiocides incorporated into plasticized polyvinyl chloride reduce adhesion of Pseudomonas fluorescens BL146 and substratum hydrophobicityxe2x80x9d, Journal of Applied Bacteriology (1996) 81, 553-560). It is disadvantageous that the biocidal effect of the active ingredients 10,10-oxybisphenoxarsine (OBPA), 2-n-octyl-4-isothiazolin-3-one (OIT), 2,3,5,6-tetrachloro-4-(methylsulphonyl)pyridine (TCMP) and N-trichloromethylthiophthalimide (NCMP) introduced into the plastic comes fully into play only if the microorganisms to be destroyed come into direct contact with the surface. The reduction of adhesion necessary for this is achieved by chance by the biocidal substances used themselves.
Substances containing silver, copper or zinc also show a biocidal effect, for example DuPont products (MicroFree(trademark) AMP). Embedded in the most varied items made from plastic, an antimicrobial effect on the surfaces of such modified plastics is noted.
Another approach is the reduction of the adhesion of proteins on surfaces. As cell membranes of microorganisms are also built up from protein components, attempts are made to prevent the accumulation of microorganisms, but particularly also of blood components, by the reduction in adhesion of proteins. An extensive state of the art describes methods for changing the properties of plastics surfaces or complete plastics parts in order to make them biocompatible. Catheters, prostheses and implants obtain biocompatible surfaces by the methods described. The deposition of biological material, for example blood cells, on prostheses or catheters or the deposition of proteins from lacrimal fluid on contact lenses can be reduced if special plastics are used for the preparation of such objects or already pre-formed objects are coated with special polymers.
WO-93/01221 describes for example polymers made from one or more radically polymerizable monomers, these polymers having groups with a permanent positive charge and groups which are able to develop a bond on surfaces.
A further approach is known from WO-94/14897, in which the biocompatibility of polymers is obtained by the coupling with polymers containing amphoteric ion groups. The amphoteric ion group is normally an ammonium salt ester; the polymer which contains this group, can be prepared via the free radical polymerisation of ethylenically unsaturated monomers together with a monomer which contains an amphoteric ion group.
Compounds which contain phosphorylcholine groups are known for their haemocompatibilizing properties and for the adhesion-reducing effect of platelets on surfaces which are treated with these compounds or have been prepared from such compounds. WO-93/21970 describes for example methods for preparing surfaces which contain groups of the general formula 
where R is the same or can be different and represents an alkyl radical with 1 to 4 C atoms and a can range from 1 to 4.
M. Humphries, J. F. Jaworzyn, J. B. Cantwell and A. Eakin described in FEMS Microbiology Letters (1987) 42, 91-101, the use of non-ionic ethoxylated and propoxylated surfactants in order to reduce the adhesion of bacteria to solid surfaces. Alcoholic ethoxylates and alkylphenolethoxylates (ICI Plastics and Petrochemicals Division, Wilton, U.K.) are used there in particular. In FEMS Microbiology Ecology (1986) 38, 299-308, M. Humphries, J. F. Jaworzyn and J. B. Cantwell described the use of biological polymers and synthetic surfactants in order to reduce the adhesion of certain bacteria species by the production of hydrophobic surfaces.
It is known however, that it is not sufficient to make the surfaces either hydrophobic or hydrophilic in order to lower the adhesion of microorganisms, as the nature of the cell walls can be completely different depending on the species.
The method of A. Pavesio, D. Renier, C. Cassinelli and M. Morra in Medical Device Technology (September 1997), 20 et seq is included in the series of coating processes, in which anti-adhesive surfaces are described by coatings with hyaluron derivatives.
More recent coating means, containing polymers with repeating units with polar or polarizable, modulating and hydrophobic fluoride-containing groups, are known from EP-0794756-A1 and EP-0794757-A1 (3M).
Preparations are also sometimes described which contain compounds which have both antimicrobial activity vis-à-vis certain bacterial strains and at the same time are intended to reduce their adhesion (Journal of Oral Rehabilitation (1988), 15, 405-411).
To summarize, the following methods are described in the state of the art:
reduction of the protein adhesion by surface treatment or by modifying the basic plastics,
destruction of the microorganisms on free surfaces by incorporated biocides.
The respective effects of these known processes are however still not satisfactory.
The object of the present invention is to prepare plastics which are improved regarding their adhesion-reducing properties or biocidal effects.
The object is achieved by specially modified plastics which are characterized in that they contain adhesion-reducing substances in such a quantity that the adhesion of microorganisms to their surface is lower by at least 50% than for non-modified plastics, and in that they contain biocidal substances in such a quantity that at least 60% of the microorganisms remaining are destroyed within 24 hours.
Permanently moist ambient conditions are present particularly in the field of dentistry. If a liquid film is located on the surface of plastics and impression materials, it is naturally permeated with proteins or microorganisms, which is extremely disadvantageous. No hopes were raised that biocidal substances would be incorporated in plastics as a result of using adhesion-reducing substances in these, as it was assumed that bacteria only briefly come into contact with the surfaces, because of the adhesion-reducing effect, at any rate too briefly for this biocidal effect to occur. Surprisingly, in spite of a clear reduction in adhesion of proteins to the surfaces of the plastics modified according to the invention, the contact time of the microorganisms with the surfaces is long enough, so that the microorganisms are predominantly destroyed.
The invention is described in detail below.
All known types of plastics can be used as plastics, depending on the modifier to be used; polyethylenes, polypropylenes, polyvinyl chlorides, polystyrenes, polycarbonates, cellophanes, cellulose acetates, polyolefins, fluorinated hydrocarbons (Teflon), polyhydroxyethyl methacrylates (PHEMA) (Hydron), polymethyl methacrylates (PMMA), polysiloxanes, polyethers and polyether silicones maybe mentioned as examples without being limitative.
A step essential to the invention is to introduce biocides into plastics. Another step essential to the invention is the incorporation of adhesion-reducing substances into the plastics or the treatment of the plastic surfaces with adhesion-reducing substances. The order of the two steps can be freely selected and is governed by the technical procedures of the manufacture of the plastics.
In order to introduce biocidal materials into the plastics, the solvent casting method is suitable for example (J. M. Schierholz, A. Rump and G. Pulverer, Arzneim. Forsch. (1997) 47, 70 et seq).
It is furthermore possible to grind the cured plastics, mix them with the biocides and press them into shape again, optionally under the action of heat. The biocide can also be added during the plastic injection process. The incorporation of biocides into dental impression materials is also conceivable. The biocide is to be added to any component of the non-cured composition. A rubber which contains biocidal properties is then obtained by the setting process. It is also advantageous with this indication that, because of the adhesion-reducing properties, blood and saliva remnants first drain off from the impression material and then microorganisms which are present are destroyed.
Substances suitable as biocides are those which release silver, silver ions, copper, copper ions, zinc or zinc ions (MicroFree(trademark) AMP, DuPont), for example copper oxides or zinc silicates, but also the free metals. of course, all other obtainable biocides can also be used. Worthy of mention are, by way of example, ciprofloxacin-HCl (Bayer AG, Leverkusen), ciprofloxacinbetaine, 10,10-oxybisphenoxarsine, 2-n-octyl-4-isothiazolin-3-one, 2,3,5,6-tetrachloro-4-(methylsulphonyl)pyridine, N-trichloromethylthiophthalimide, chlorohexidine, long-chained bisphenol esters (U.S. Pat. No. 3,427,345; 3M), sodium fluoride in combination with dodecylamine or other organic amines, benzalkonium chloride, cetylpyridinium chloride, 4-chloro-2-(2,4-dichlorophenoxy)phenol (Triclosan), complex or simple fluorides such as SnF2, KZnF3, ZnSnF4, Zn(SnF3)2, potassium or zirconium hexafluorotitanate, N-oxides of saturated N-containing heterocycles substituted by quinolonecarboxylic acids or napthyridonecarboxylic acids (EP-0828715-A1). The biocides are incorporated in quantities of approx. 0.001 to 20 pts. by wt., preferably 0.01 to 10 pts. by wt., per 100 pts. by wt. of the total material.
Plastics or surfaces suitable as adhesion-reducing substances and methods for preparing adhesion-reducing plastics or surfaces are for example those based on phosphorylcholine or phosphorylethanolamine (WO-93/21970, EP-0199790-B1, WO-94/14897, WO-93/01221, EP-0641226-B1, EP-0518959-B1, WO-90/09384, EP-0157469-B1, WO-94/16749, WO-94/16748) or also those based on polyesters made from units which are derived from glycerophosphorylcholine or glycerophosphorylethanolamine and polyfunctional acids or their derivatives (EP-0275293-B1). The adhesion-reducing substances are introduced or applied as surface coating in quantities of approx. 0.05 to 50 pts. by wt., preferably 0.1 to 20 pts by wt., per 100 pts. by wt. of the total material.
Generally, the surface coating is carried out by dissolving the reactive agent in a compatible solvent, treating the surface with the solution and then drying it. Where necessary, the surface must be functionalzied; this can occur via known etching or derivatizing techniques, such as plasma discharge (see xe2x80x9cChemical Reactions of Polymersxe2x80x9d, Ed. E. M. Fettes (1964), Interscience, London). The diverse processes can be deduced from the previously mentioned documents, the disclosure content of which is thereby to be wholly included.
The plastics according to the invention are suitable for the preparation of plastics and plastic parts to be used in dentistry and dental engineering, for example housing parts of mixing or polymerisation equipment, also light rods of light polymerisation equipment, primary and secondary packaging materials for dental materials, application instruments for dental materials, for example for applying filling materials, as well as for dental materials themselves, for example impression materials. They are generally suitable for all plastic parts which are used when practising the dental or dental engineering profession.